JP2008211760A - Modulation system estimation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modulation system estimation apparatus correctly estimating a modulation system even when a device on a reception side or on a transmission side is moving at a high speed. <P>SOLUTION: The modulation system estimation apparatus for estimating the modulation system of signals transmitted by other radio device comprises, for instance: a frequency deviation-transmission rate estimation part 13 for successively estimating the carrier frequency of reception signals; a frequency deviation correction part 12 for correcting the frequency deviation of the reception signals on the basis of the carrier frequency estimated in the frequency deviation-transmission rate estimation part 13; and a modulation system estimation part 14 for estimating the modulation system on the basis of the carrier frequency estimated in the frequency deviation-transmission rate estimation part 13 and the reception signals after correcting the frequency deviation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a modulation scheme estimation apparatus that estimates a modulation scheme of an unknown signal transmitted by a radio.

  Patent Document 1 below describes a digital phase modulation method determination display method for determining a digital phase modulation method of an unknown signal transmitted by a wireless device. In this document, an estimated carrier frequency is obtained from the frequency domain data of an unknown digital phase modulation signal, a detection operation is performed, a symbol point for phase modulation is obtained, and then a true carrier frequency is obtained, thereby detecting again. Perform an operation to display the exact symbol point on the coordinate plane. By this display, an unknown digital phase modulation method can be determined.

JP-A-9-298567

  For example, when a receiving side device that estimates a modulation scheme or a transmitting side device that is a transmission source is moving at high speed, the received signal is usually accompanied by a change in moving direction or a moving speed. Shift frequency.

  On the other hand, in the conventional technique described in Patent Document 1, after performing rough estimation of the carrier frequency, synchronous detection is performed by changing the carrier frequency, and the carrier frequency when the signal point variation is the least is assumed to be correct. A case where the received signal is frequency-shifted as described above is dealt with by performing processing. However, in the above processing, it takes time to estimate the modulation scheme, and it may be impossible to follow the fluctuation of the carrier frequency, and in such a case, the correct modulation scheme cannot be estimated. There was a problem.

  The present invention has been made in view of the above, and obtains a modulation scheme estimation apparatus capable of correctly estimating a modulation scheme even when a reception-side or transmission-side apparatus is moving at high speed. For the purpose.

  In order to solve the above-described problems and achieve the object, a modulation scheme estimation apparatus according to the present invention is a modulation scheme estimation apparatus that estimates a modulation scheme of a signal transmitted by another radio, for example, a received signal. Carrier frequency estimation means for sequentially estimating the carrier frequency of the received signal, frequency deviation correction means for correcting the frequency deviation of the received signal based on the carrier frequency estimated by the carrier frequency estimation means, and carrier frequency estimation means Modulation scheme estimating means for estimating the modulation scheme of the received signal based on the estimated carrier frequency and the received signal after frequency deviation correction.

  According to the present invention, there is an effect that the modulation scheme can be correctly estimated even when the reception-side device or the transmission-side device serving as the transmission source is moving at high speed.

  Embodiments of a modulation scheme estimation apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of a receiving apparatus that operates as a modulation scheme estimating apparatus according to the present invention, and includes an antenna 10, a receiving section 11, a frequency deviation correcting section 12, a frequency deviation / transmission rate estimating section 13, and a modulation scheme. An estimation unit 14 is provided.

  Hereinafter, the operation of the modulation scheme estimation apparatus will be described with reference to the drawings. First, the receiving unit 11 performs processing such as band limitation, down-conversion, analog / digital conversion, etc., on the analog signal received by the antenna 10, and receives the intermediate frequency or baseband received signal Y ( n) is output.

Next, the frequency deviation / transmission rate estimation unit 13 sequentially estimates the frequency deviation f and the transmission rate R of the reception signal Y (n) output from the reception unit 11. The frequency deviation correction unit 12 corrects the reception signal Y (n) by the following equation (1) based on the frequency deviation f estimated by the frequency deviation / transmission rate estimation unit 13.
Z (n) = Y (n) × exp (−j · 2π · f · n) (1)
Z (n) is a corrected received signal, and j is the square root of -1.

  Then, the modulation method estimation unit 14 estimates the modulation method based on the received signal Z (n) corrected by the frequency deviation correction unit 12.

  Next, the configuration and processing of the frequency deviation / transmission rate estimation unit 13 in the modulation scheme estimation apparatus will be described. FIG. 2 is a diagram illustrating a configuration example of the frequency deviation / transmission rate estimation unit 13. The frequency deviation / transmission rate estimation unit 13 includes a frequency domain conversion unit 20, an averaging processing unit 21, and a threshold calculation unit 22. , A frequency deviation calculator 23 and a transmission rate calculator 24 are provided.

  The frequency domain transform unit 20 transforms the received signal into a frequency domain power spectrum by an operation such as discrete Fourier transform (DFT) or fast Fourier transform (FFT).

  As shown in FIG. 3, the averaging processing unit 21 averages the power spectrum output from the frequency domain conversion unit 20 for each power of the same frequency, and further averages over a certain frequency range as shown in FIG. Turn into. 3 and 4 are diagrams illustrating an example of the averaging process. As a result, a highly accurate power spectrum can be calculated while suppressing variations due to noise and the like.

  The threshold value calculation unit 22 outputs, for example, a half point of the maximum power of the power spectrum smoothed by averaging to the transmission rate calculation unit 24 and the frequency deviation calculation unit 23 as a threshold value. Note that the threshold values output to the transmission rate calculation unit 24 and the frequency deviation calculation unit 23 do not have to be the same value. For example, the threshold value output to the frequency deviation calculation unit 23 is 2/3 of the maximum power. It may be.

The frequency deviation calculator 23 sets the center of the point (A, B) where the threshold obtained from the threshold calculator 22 and the power spectrum intersect as the frequency deviation amount. That is, when the frequency at the lower frequency point where the power spectrum and the threshold value intersect is A and the frequency at the higher frequency point where the power spectrum intersects is B, the frequency deviation amount f is calculated by the following equation (2). .
f = (A + B) / 2 (2)

Further, the transmission rate calculation unit 24 calculates the difference between the points (A, B) where the threshold value obtained from the threshold value calculation unit 22 and the power spectrum intersect, and calculates the transmission bandwidth obtained as a result of the calculation. The transmission rate. That is, when the frequency at the lower frequency point where the power spectrum and the threshold value intersect is A and the frequency at the higher frequency point where the power spectrum intersects is B, the transmission rate R is calculated by the following equation (3).
R = B−A (3)

  Next, the configuration and processing of the modulation scheme estimation unit 14 in the modulation scheme estimation apparatus will be described. FIG. 5 is a diagram illustrating a configuration example of the modulation scheme estimation unit 14. The modulation scheme estimation unit 14 includes filter units 30 and 32, a power variation calculation unit 31, a phase variation calculation unit 33, and a modulation scheme determination unit. 34 is provided.

  The filter unit 30 and the filter unit 32 perform a filtering process on the corrected reception signal output from the frequency deviation correction unit 12 to remove unnecessary components outside the signal band. In addition, in the filter part 30 and the filter part 32, the frequency width when performing band limitation does not need to be the same, and the filter characteristics do not have to be the same. On the contrary, when the same frequency width and the same filter characteristics are used, the filter processing may be executed by sharing one filter unit.

  The power fluctuation amount calculation unit 31 calculates the power fluctuation amount of the received signal after the filter process, and outputs the fluctuation amount. FIG. 6 is a diagram illustrating an example of a method for calculating the power fluctuation amount. Here, the received signal 40 is divided into blocks 41, 42, and 43 having appropriate lengths, and the ratio between the average value of the maximum power values 45, 47, and 49 and the average value of the minimum power values 44, 46, and 48 in each block. Is the amount of power fluctuation.

  On the other hand, the phase variation calculation unit 33 calculates the symbol length T based on the transmission rate R output from the transmission rate calculation unit 24, and calculates the mean square of the phase deviation of the symbol interval in the received signal as the phase variation amount. .

  Here, a method of calculating the phase fluctuation amount will be specifically described. FIG. 7 is a diagram illustrating an example of a method of calculating the phase fluctuation amount.

  First, in the phase fluctuation amount calculation unit 33, the sampling point 51 at which the power becomes maximum between the head and the range Q of the received signal 50: z (n) after the band limitation output from the filter unit 32 is performed. Is detected. Note that the range Q is longer than the symbol length T. The symbol time length T is calculated as, for example, a value obtained by dividing the sample rate of the received signal by the transmission rate R.

Next, the phase deviation P (1) between the received signal z (N1) at the sample point 51 and the received signal z (N1 + T) at the sample point 52 separated from the sample point 51 by the symbol time length T is Calculated according to equation (4).
P (1) = MOD [z (N1 + T) × CONJG [z (N1)] + π / 2, π] −π / 2
(4)
CONJG [x] is a complex conjugate of the complex number x, and MOD [x, π] represents the remainder when x is divided by π in the range of 0 to less than π.

  Next, the sample point 53 where the power is maximum in the range of the length L is determined with the received signal z (N1 + T) as the center. Note that L is shorter than the symbol length T.

Next, the phase deviation P (2) between the received signal z (N2) at the sample point 53 and the received signal z (N2 + T) at the sample point 54 separated from the sample point 53 by the symbol time length T is Calculated according to equation (5).
P (2) = MOD [z (N2 + T) × CONJG [z (N2)] + π / 2, π] −π / 2
... (5)

  Then, the above phase deviation calculation process is repeatedly performed on the received signal, and finally, the mean square of the phase deviation P (m) is calculated as the phase fluctuation amount.

  Thereafter, the modulation scheme determination unit 34 determines the modulation scheme based on the power variation output from the power variation calculation unit 31 and the phase variation output from the phase variation calculation unit 33. FIG. 8 is a diagram illustrating an example of a modulation method determination method. As shown in FIG. 8, on the two-dimensional plane of the power fluctuation amount and the phase fluctuation amount, areas (corresponding to the modulation schemes # 1 to # 4 shown in the figure) corresponding to each modulation scheme are determined in advance. The determination unit 34 determines the modulation method according to which region the input power fluctuation amount and phase fluctuation amount are in. On the other hand, if the input power fluctuation amount and phase fluctuation amount do not fall in any region associated with the modulation scheme, that is, if it does not apply to any modulation scheme, determination is not possible.

  Note that the modulation scheme determination unit 34 may set the modulation scheme as a determination result only when the determination value of the modulation scheme continues for S times, and may not be able to determine otherwise. Thereby, it is possible to obtain a better determination accuracy.

  In addition to the two-dimensional plane, it is also possible to extend so that the modulation scheme is determined by a region in a multidimensional space using another feature amount. For example, Shinbo et al., “Identification of Digital Modulation System with Carrier Frequency Offset Using Coupling Moment” (The IEICE Transactions B, Vol.J89-B, No.10, pp.1971-1980, 2006) It is possible to determine the modulation method by the region in the multidimensional space using the coupling moment described in October), the decision variable of the differential coupling moment method, the decision variable of the signal point shift differential coupling moment method, etc. .

  Further, when the transmission rate is known in the modulation scheme determination unit 34 or when the transmission rate information is not necessary for estimation of the modulation scheme, the frequency deviation / transmission rate estimation unit 13 can be configured not to estimate the transmission rate. It is. In this case, the frequency deviation / transmission rate estimation unit 13 has a configuration in which the transmission rate calculation unit 24 is omitted.

  In addition, this embodiment can estimate not only a digital modulation signal but also an analog modulation signal.

  Thus, in the present embodiment, the frequency deviation amount of the received signal is estimated, the frequency rotation of the received signal is corrected based on the estimated amount, and then the power fluctuation calculated using the corrected received signal The modulation scheme is estimated based on the amount and the phase fluctuation amount. As a result, the modulation scheme can be correctly estimated even when the receiving apparatus or the transmitting apparatus serving as the transmission source is moving at high speed.

  In addition, since it is not necessary to perform processing at a predetermined sample rate in the modulation scheme estimation unit 14, it can be realized without controlling the sample rate at the time of analog / digital conversion of the reception unit 11. For this reason, the configuration can be simplified, and it is not necessary to spend time for the processing for controlling the sample rate, and the modulation scheme can be determined in a short time.

Embodiment 2. FIG.
Next, the second embodiment will be described. In Embodiment 1 described above, the modulation scheme is estimated without considering the condition of the communication channel with the transmitter, but the estimation accuracy is improved by estimating the modulation scheme in consideration of the communication channel condition. It is possible to make it.

  FIG. 9 is a diagram illustrating a configuration example of a reception apparatus that operates as the modulation scheme estimation apparatus according to the second embodiment. The receiving apparatus according to the present embodiment adds a channel condition estimation unit 15 and a parameter control unit 16 to the receiving apparatus according to the first embodiment (see FIG. 1), and performs modulation instead of the modulation scheme estimation unit 14. A configuration including a method estimation unit 14a is adopted. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  The modulation scheme estimation unit 14a estimates a modulation scheme using parameters set by the parameter control unit 16 described later. The modulation scheme estimation process is the same as the estimation process performed by the modulation scheme estimation unit 14 (see FIG. 5) described in the first embodiment. That is, the modulation scheme estimation unit 14a is the same as the modulation scheme estimation unit 14 of Embodiment 1 except that the internal parameters are different.

  The communication path state estimation unit 15 estimates the state of the communication path between the transmitter and the own apparatus. Specifically, S / N (C / N) and the maximum Doppler frequency are estimated as the channel conditions. Instead of estimating both the S / N and the maximum Doppler frequency, either one may be estimated. Moreover, when estimating, a well-known estimation technique is used.

  The parameter control unit 16 uses the parameter (at least one of S / N and the maximum Doppler frequency) estimated by the channel condition estimation unit 15 as a parameter to be used for the modulation scheme estimation process in the modulation scheme estimation unit 14a. Control. Specifically, the length of the signal used for calculating the feature amount (corresponding to the length of the signal used for calculating the power fluctuation amount and the phase fluctuation amount once), and each modulation method shown in FIG. The region and the filter bandwidth of the filter unit 30 and the filter unit 32 are set to values selected from a plurality of values prepared in advance.

  As a result, the modulation scheme estimation unit 14a estimates the modulation scheme under the optimum conditions (parameters) set by the parameter control unit 16 and corresponding to the channel conditions.

  As described above, according to the present embodiment, the internal parameters used in the modulation scheme estimation processing in the modulation scheme estimation unit are appropriately changed according to the estimation result of the channel status. Therefore, the modulation scheme can be estimated with higher accuracy than when the modulation scheme is estimated using the same parameters (the first embodiment described above).

  When the communication path condition is known, the user can prevent the estimation error of the modulation scheme due to the influence of the estimation error by setting the parameter.

Embodiment 3 FIG.
Next, Embodiment 3 will be described. In the second embodiment described above, the parameters used in the modulation scheme estimation process are changed in consideration of the communication channel condition. However, the parameters used in the frequency deviation estimation process and the transmission rate estimation process are further changed. It may be changed.

  FIG. 10 is a diagram illustrating a configuration example of a reception apparatus that operates as the modulation scheme estimation apparatus according to the third embodiment. The receiving apparatus of the present embodiment replaces the frequency deviation / transmission rate estimation unit 13 and parameter control unit 16 of the receiving apparatus of Embodiment 2 (see FIG. 9) with a frequency deviation / transmission rate estimation unit 13b and parameter control unit. The structure provided with 16b is taken. Since other configurations are the same as those of the second embodiment, the same reference numerals are given and description thereof is omitted.

  The frequency deviation / transmission rate estimation unit 13b estimates the frequency deviation f and the transmission rate R using parameters set by the parameter control unit 16b described later. The estimation processing of each information is the same as the estimation processing by the frequency deviation / transmission rate estimation unit 13 (see FIG. 2) shown in the first embodiment. That is, the frequency deviation / transmission rate estimation unit 13b is the same as the frequency deviation / transmission rate estimation unit 13 of the first embodiment except that the internal parameters are different.

  In addition to the parameters (parameters used for modulation scheme estimation processing in the modulation scheme estimation section 14a) controlled by the parameter control section 16 shown in the second embodiment, the parameter control section 16b includes a frequency deviation / transmission rate estimation section 13b. The parameters used in the information (frequency deviation, transmission rate) estimation process in the above are controlled based on the information (at least one of S / N and the maximum Doppler frequency) estimated by the channel condition estimation unit 15. Specifically, the length of the signal used for feature quantity calculation, the area of each modulation method shown in FIG. 8, the filter bandwidths of the filter unit 30 and the filter unit 32, and the averaging processing unit 21 perform averaging. The length to be performed (the length of the time frame, which is a unit of averaging shown in FIG. 3), the threshold value used for calculating the transmission rate in the transmission rate calculation unit 24, and the frequency deviation calculation unit 23 The threshold value used for the calculation of the frequency deviation is set to a value selected from a plurality of values prepared in advance.

  However, as shown in the first embodiment, the threshold value calculation unit 22 determines the threshold value used in the transmission rate calculation unit 24 and the threshold value used in the frequency deviation calculation unit 23. The unit 16b controls the threshold value by setting a value (a value indicating the relationship between the maximum power and the threshold value) to be referred to when the threshold value calculating unit 22 determines each threshold value.

  As a result, the frequency deviation / transmission rate estimation unit 13b and the modulation scheme estimation unit 14a perform the above-described processing under the optimum conditions (parameters) set by the parameter control unit 16 and corresponding to the communication path conditions.

  As described above, in the present embodiment, the internal parameters used in the frequency deviation and transmission rate estimation processing by the frequency deviation / transmission rate estimation unit are appropriately changed according to the estimation result of the communication channel state. The frequency deviation and the transmission rate can be estimated with higher accuracy than in the case where the modulation scheme is estimated with the same parameter regardless of the communication channel condition (the first embodiment described above). As a result, in the latter modulation scheme estimation, the modulation scheme can be estimated with higher accuracy than in the second embodiment.

  When the communication path condition is known, the user can prevent the estimation error of the modulation scheme due to the influence of the estimation error by setting the parameter.

  As described above, the modulation scheme estimation apparatus according to the present invention is useful for a reception-side communication apparatus that constitutes a wireless communication system, and particularly for a communication apparatus that estimates a modulation scheme of an unknown signal transmitted by a radio. Is suitable.

It is a figure which shows the structural example of the receiver which operate | moves as a modulation system estimation apparatus concerning this invention. It is a figure which shows the structural example of a frequency deviation and a transmission rate estimation part. It is a figure which shows an example of an averaging process. It is a figure which shows an example of an averaging process. It is a figure which shows the structural example of a modulation system estimation part. It is a figure which shows an example of the calculation method of electric power fluctuation amount. It is a figure which shows an example of the calculation method of a phase fluctuation amount. It is a figure which shows an example of the determination method of a modulation system. 6 is a diagram illustrating a configuration example of a receiving device that operates as a modulation scheme estimation device according to Embodiment 2. FIG. FIG. 10 is a diagram illustrating a configuration example of a receiving apparatus that operates as a modulation scheme estimation apparatus according to Embodiment 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Antenna 11 Receiving part 12 Frequency deviation correction | amendment part 13, 13b Frequency deviation and transmission rate estimation part 14, 14b Modulation system estimation part 15 Communication channel condition estimation part 16, 16b Parameter control part 20 Frequency domain conversion part 21 Averaging process part 22 Threshold calculation unit 23 Frequency deviation calculation unit 24 Transmission rate calculation unit 30, 32 Filter unit 31 Power variation calculation unit 33 Phase variation calculation unit 34 Modulation method determination unit

Claims (7)

A modulation method estimation device for estimating a modulation method of a signal transmitted by another radio device,
Carrier frequency estimation means for sequentially estimating the carrier frequency of the received signal;
A frequency deviation correcting means for correcting a frequency deviation of the received signal based on the carrier frequency estimated by the carrier frequency estimating means;
Based on the carrier frequency estimated by the carrier frequency estimation means and the received signal after frequency deviation correction, a modulation method estimation means for estimating the modulation method of the received signal;
A modulation scheme estimation apparatus comprising: The carrier frequency estimation means includes
A frequency domain converting means for converting the received signal into frequency domain information;
Averaging means for averaging the frequency domain information output by the frequency domain transforming means by frequency and time;
Threshold calculation means for calculating a threshold for specifying the signal band of the received signal based on the averaging result output by the averaging processing means;
Carrier frequency calculation means for calculating a carrier frequency based on the threshold value output by the threshold calculation means;
The modulation scheme estimation apparatus according to claim 1, further comprising: The modulation scheme estimation means includes
Power fluctuation amount calculating means for calculating the power fluctuation amount of the received signal after frequency deviation correction;
Based on the carrier frequency estimated by the carrier frequency estimation means, phase fluctuation amount calculation means for calculating the phase fluctuation amount of the received signal after frequency deviation correction;
A modulation scheme determination unit that determines a modulation scheme based on the power variation amount calculated by the power variation amount calculation unit and the phase variation amount calculated by the phase variation amount calculation unit;
The modulation scheme estimation apparatus according to claim 1, further comprising:   The power fluctuation amount calculation means divides the received signal at an appropriate time interval, calculates the maximum value and the minimum value of the power within the range of each received signal after the division, and obtains the maximum value and the minimum value obtained. 4. The modulation scheme estimation apparatus according to claim 3, wherein an average ratio of each value is output as a power fluctuation amount. In the phase variation calculation means,
First, the point at which the power of the received signal is maximum in a predetermined first time range (> symbol length) is defined as the first reference point, and the received signal at the first reference point and 1 from the first reference point. Calculating a phase deviation from a received signal at a point separated by a symbol length, and performing a first phase deviation calculation process for calculating a square of the phase deviation;
Next, a point at which the power of the received signal is maximum in a predetermined second time range (<symbol length) before and after the point separated by one symbol length from the first reference point is defined as a second reference point. A second phase deviation calculation that calculates a phase deviation between the received signal at the second reference point and a received signal at a point one symbol length away from the second reference point, and calculates the square of the phase deviation. Process,
Thereafter, the same process as the second phase deviation calculation process is repeatedly performed on the received signal, and the average value of the squares of the phase deviations obtained by the respective phase deviation calculation processes is used as the phase fluctuation amount. The modulation method estimation apparatus according to claim 3 or 4, further,
Parameter control means for adjusting an internal parameter of the modulation scheme estimation means to an appropriate value based on a communication path condition from the other wireless device to the own device,
The modulation method estimation apparatus according to claim 1, comprising: The parameter control means includes
7. The modulation scheme estimation apparatus according to claim 6, further comprising adjusting an internal parameter of the carrier frequency estimation means to an appropriate value based on the communication path condition.

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